Patients with pulmonary infiltrates receive more than half of the antibiotics prescribed in the ICU. Many of these patients receive antibiotics for suspected, but not proven, respiratory infections. Yet many of these patients with abnormal radiographs actually have a non-infectious etiology. Although pneumonia is the most common hospital acquired infection in ICU patients, it is difficult to diagnose definitively because the diagnosis relies heavily on radiographic findings that correlate poorly with clinical pneumonia. But because of the attributable mortality associated with nosocomial pneumonia, the risk of missing a treatable infection often outweighs the perception of minimal risk antibiotic therapy. Consequently, overuse or inappropriate use of antibiotics for the treatment of suspected pneumonia is widespread in this subset of patients, and the emergence of antimicrobial resistant bacteria as a result of antibiotic overuse is increasingly common. Progress Report: Final approval from the BAMSG Steering Committee has been obtained. An IND has been obtained. The NIAID IRB approved this protocol. In addition 5 other sites have obtained IRB approval and have had their site initiation visits from the biostatistics support and coordinating center (BAMBU). Seven sites are awaiting either IRB approval or their site initiation visit. The study is currently enrolling patients with a projected enrollment of 420 patients in total. This study was closed in April 2007.